1. Field of the Invention
The present invention relates to telephony and more particularly to a telephone hold circuit which places the telephone on-hold upon momentary actuation of the telephone hook switch.
2. Prior Art
Telephones having a hold feature are well known in private automatic exchange installations utilizing multi-line pushbutton telephones. Such apparatus is disclosed in U.S. Pat. No. 3,909,553 issued to Marshall, U.S. Pat. No. 3,909,554 issued to Reed, U.S. Pat. No. 4,056,695 issued to Angner et al., U.S. Pat. No. 3,925,625 issued to Angner et al. and U.S. Pat. No. 3,965,308 issued to Jones et al. In addition, hold circuitry suitable for use with ordinary domestic telephones is disclosed in U.S. Pat. No. 3,246,082 issued to Levy and U.S. Pat. No. 4,011,413 issued to Phillips.
The Phillips reference is typical of the prior art hold circuits and is perhaps the most relevant reference. Phillips discloses a hold circuit suitable for use with ordinary domestic telephones. As can be seen in FIG. 1 of the Phillips reference, a separate hold switch module 21 is attached to the housing of each telephone on the line. The user places a call on hold by depressing a momentary contact push-button switch 31 projecting from the housing while simultaneously returning the receiver to the cradle. Once the receiver is in the cradle, the push-button is released and the call is placed on hold.
Although the Phillips reference discloses a relatively simple circuit for providing a hold feature to a pre-existing telephone, such circuit possesses various shortcomings. Perhaps the most serious shortcoming is the requirement that each telephone be provided with a separate hold switch and hold switch module.
The novel hold circuit disclosed herein overcomes the disadvantage of the prior art circuits including the circuit disclosed by Phillips. By way of example, all of the circuitry of the subject invention may be enclosed in a single module which may be placed within the housing in one of the telephones. The circuit is simply connected across the telephone lines and requires no modification of any of the telephones. Most importantly, the telephone hook switch is used to place the telephone in a hold condition so as to eliminate the necessity of a separate hold switch. Further advantages of the subject invention will become apparent from the subsequent detailed description.